The invention relates to a clamping system for a fuel cell stack.
A fuel cell is an electrochemical device that converts chemical energy that is produced by a reaction directly into electrical energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), often called a polymer electrolyte membrane, that permits only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is reacted to produce hydrogen protons that pass through the PEM. The electrons produced by this reaction travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions are described by the following equations:
H2xe2x86x922H++2exe2x88x92
at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O
at the cathode of the cell.
A typical fuel cell has a terminal voltage near one volt DC. For purposes of producing much larger voltages, several fuel cells may be assembled together to form an arrangement called a fuel cell stack, an arrangement in which the fuel cells are electrically coupled together in series to form a larger DC voltage (a voltage near 100 volts DC, for example) and to provide a larger amount of power.
The fuel cell stack may include flow plates (graphite composite or metal plates, as examples) that are stacked one on top of the other, and each plate may be associated with more than one fuel cell of the stack. The plates may include various surface flow channels and orifices to, as examples, route the reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells.
For purposes of directing the reactant, coolant and product flows into and out of the flow channels of the flow plates, the flow plates typically include aligned openings to form manifold passageways in the stack. Gaskets may be located between the flow plates to seal off these manifold passageways and seal off the flow channels that are formed by the flow plates.
FIG. 1 depicts an exemplary fuel cell stack assembly 10, an assembly that includes a stack 12 of flow plates that are clamped together under a compressive force. To accomplish this, the assembly 10 typically includes end plate 16 and spring plate 20 that are located on opposite ends of the stack 12 to compress the flow plates that are located between the plates. Besides the end plate 16 and spring plate 20, the assembly 10 may include a mechanism to ensure that a compressive force is maintained on the stack 12 over time, as components within the stack 12 may settle, or flatten, over time and otherwise relieve any applied compressive force.
As an example of this compressive mechanism, the assembly 10 may include another end plate 14 that is secured to the end plate 16 through tie rods 18 that extend through corresponding holes of the spring plate 20. The spring plate 20 is located between the end plate 14 and the stack 12, and coiled compression springs 22 may reside between the end plate 14 and spring plate 20. The tie rods 18 slide through openings in the spring plate 20 and are secured at their ends to the end plates 14 and 16 through nuts 15 and 17. Due to this arrangement, the springs 22 remain compressed to exert a compressive force on the stack 12 over time even if the components of the stack 12 compress.
To establish connections for external conduits (hoses and/or pipes) to communicate the reactants, coolants and product with the manifold passageways of the stack 12, the assembly 10 may include short connector conduits, or pipes 24, that may be integrally formed with the end plate 16 to form a one piece end plate assembly (for example, pipes 24 may be welded to end plate 16). The pipes 24 form the complex part of the end plate assembly, making the end plate assembly difficult to mass manufacture due to the high cost of the required materials and the multiple operations that may be needed to manufacture the end plate assembly.
Thus, there is a continuing need for an arrangement that addresses one or more of the problems that are stated above, or that improves such functionality and features.
In an embodiment of the invention, a fuel cell stack assembly includes a stack of fuel cell flow plates that include fluid passageways; pipes to communicate fluids with the fluid passageways; an end plate; and a dielectric manifold. The end plate supports a compressive load to compress the stack, and the end plate includes openings. The manifold is located between the end plate and the stack to communicate the fluids between the pipes and the fluid passageways. The manifold at least partially extends through the openings in the end plate to form a sealed connection between the manifold and the pipes.
In another embodiment of the invention, a fuel cell stack assembly includes first and second end plates; a fuel cell stack of flow plates; at least one spring; and tie rods. The stack is located between the first and second end plates, and the spring(s) have ends that extend across different edges of the first end plate. Each tie rod has a first end that is connected to one of the ends of said at least one spring and a second end that is connected to the second end plate to cause the first and second end plates to apply a compressive force to the stack.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.